Cross-sectional view of the posterior fossa at the level of the medulla. The brainstem has been transected at the rostral medulla; for orientation, the bottom of the image is ventral. Cranial nerves IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal) originate as medullary nuclei. Cranial nerves IX and XI exit the ventrolateral medulla and course toward the jugular foramen in the lateral medullary cistern. The posterior inferior cerebellar artery (PICA) is visible on the left as a branch of the vertebral artery and in this image traverses the left cranial nerve IX-X-XI complex near the jugular foramen. Cranial nerve XII is visible inferiorly entering the hypoglossal canal, just rostral to the occipital condyle and near the origin of PICA. Cranial nerve VI (abducens) has been cut and can be visualized near the midline prior to entering Dorello’s canal, and cranial nerve V (trigeminal) has similarly been transected prior to entering Meckel’s cave. Bilateral anterior inferior cerebellar arteries (AICA) are visible as the most proximal branches of the basilar artery. (Image courtesy of AL Rhoton, Jr.)